The Liberal Democrats are expecting the largest conference in the party's 22-year history, starting on Saturday in Liverpool. Media attendance will be up 62% and overall numbers of delegates up to 6,200 – a 40% increase on last year as the party grapples with its rise from the UK's third largest party to government.

The Lib Dem with the task of maintaining links between his party high command and the grass roots – Norman Lamb – told journalists in a briefing yesterday he expected the party to be celebrating the fact that for the first time in over half a century it was in government.

But Lib Dem activists, whose conference has long been celebrated as the most consultative, have already tabled motions to register unease with the direction Tory policies are taking the coalition. On Sunday, before the leader Nick Clegg delivers his speech on Monday, a vote will be taken at the conference expressing concern over the policy to set up new free schools. The motion asserts that they are "socially divisive".

Asked whether there would be unhappiness from some Lib Dem activists, Lamb said implementing policy rather than talking about it was "at the end of the day, what parties are for". He acknowledged the party members were used to being listened to: "We have a vibrant party that has a soul and is determined to debate key issues." But he added that times had changed: "Policy might have been changed but nothing in the real world changed with it. We now have a unique opportunity."

He assured the grassroots that the policy-making process of their party conference would continue to have an effect. While they will be unable to effect changes to join Lib Dem-Tory policies already agreed, they would have an influence on elements of the coaliton document not yet finalised. He said ideas arrived at during the conference could later be drawn upon. "Conference makes party policy and party policy continues to be made and delivered," he said.

Lamb denied the conference agenda had been filled with Lib Dem cabinet ministers in order to shut down debate on the party's role in a coalition with the Tories, and also shot down the idea that they had been losing votes to Labour, with the ratio of those joining the party compared with those leaving running at a ratio of 9:1 since the general election.